This invention relates to a magnetic recording medium and a process for preparing the magnetic recording medium, and more particularly to a magnetic recording medium having an imporved magnetic layer and a process for preparing the same.
The conventional magnetic recording system is based mainly on magnetizing a recording medium in an intraplanar direction, and has a problem of demagnetization due to more intensification of a demagnetizing field on the recording magnetization with increasing recording density. To overcome this problem, a perpendicular magnetic recording system has been proposed, where a recording medium is magnetized in a direction perpendicular to the film surface to eliminate demagnetization in the region of high recording density.
The perpendicular magnetic recording medium can be classified into two groups: a monolayer film medium whose magnetic layer is a perpendicularly magnetizable single layer, and a double layer film medium composed of a soft magnetic layer and a perpendicularly magnetizable layer provided thereon.
The soft magnetic layer of the double layer film medium serves to focue the magnetic field of a magnetic head on a recording region and stabilize the recording magnetization. Consequently the reproduction output power of the double layer film medium is much increased, as compared with that of the monolayer film medium (U.S. Pat. No. 4,210,946).
Intensive research and development of double layer film media for perpendicular recording has been so far made from such viewpoints. According to a specific structure, a soft magnetic thin film of permalloy, Co-based amorphous material, etc. is provided on a substrate, and a perpendicularly magnetizable film of Co-Cr alloy is provided on the soft magnetic thin film. However, a magnetic recording medium having such a metallic thin film as a layer has such problems that it is less flexible and is more liable to be scarred with sliding of a magnetic head.
Furthermore, a magnetic recording medium having such a structure that a dispersion of soft magnetic powder in a binder is coated onto a non-magnetic substrate and a perpendicular magnetizable layer is provided on the soft magnetic powder layer has been proposed, but has such problems that a higher packing density and uniform dispersion of the soft magnetic powder cannot be obtained, resulting in increased number of dropouts in the region of high recording density. Furthermore, it is difficult to obtain a uniform thickness of the soft magnetic powder layer as coated, and thus the surface properties of the perpendicularly magnetizable layer to be formed thereon are deteriorated, resulting in larger spacing loss. That is, it has been so far impossible in the prior art processes to prepare a magnetic recording medium of the double layer film type for perpendicular recording having a uniform quality on a mass-production scale.